Numerical Networking Definitions & Concepts...

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The ampersand is used to indicate special characters in HTML (Hypertext Markup Language) documents -- that is, documents for the World Wide Web. For example, "&" specifies the ampersand character (&); "ö" specifies a lowercase o with an umlaut, or dieresis, mark (ö) over the o.

Angle brackets are used in pairs to surround markup tags in HTML (Hypertext Markup language) documents for the World Wide Web. For example <P> indicates a paragraph break; <B> and </B> indicate the start and end of a section that is to be displayed in boldface.

In serveral operating systems, the asterisk serves as a wildcard character: to represent one or more characters, such as in a file name or extension. For example, a* matches act, actor, and and, but not band.

In pattern matching involving regular expressions, the asterisk matches the occurrences of the single character immediately preceding it. For example, ba*th matches bth, bath, and baaaaath, but not bbath.

In e-mail and in other contexts that use plain text, asterisks are sometimes used around words or phrases to indicate emphasis. For example, "I *really* want to emphasize the second word in this sentence."

The at sign is used to separate the username from domain specifiers in e-mail addresses. For example mels@golemxiv.mit.edu would indicate someone with the username mels on a computer named golemxiv at MIT.

In some operating systems, such as DOS, OS/2, and NetWare, the backslash character separates directory names or directory and file names in a path statement. By itself, the backslash represents the root directory in these operating systems.

In various programming and editing contexts, the backslash is used to escape the character that follows. For example, \n is an escape code to indicate a newline character in many operating environments.

In URLs (Uniform Resource Locators), double slash caracters separate the protocol from the site and document names. For example, if it existed,

http://examplehost.ucsc.edu/

filename.html

would refer to a file named filename.html residing on the examplehost machine at the University of California at Santa Cruz. To get to teh this file, you would use a server that supports the HTTP (HyperText Transport Protocol).

Used as an abbreviation for the prefix micro, as in (sec for microsecond and µm for micrometer. This order of magnitude correcsponds to 2^-20, which is roughly 10^-6, or one-millionth. Also see "Order of Magnitude".

In hierarchically organized directory systems, such as those used by UNIX, DOS, and OS/2, . and .. refer to the current and the parent directories, respectively. In pattern matching involving regular expressions, the . matches any single caracter, except a newline character.

In many operating systems, a question mark serves as a wildcard character that represents a single character, such as in a file or directory name.

The slash (also known as a forward slash or a virgule) separates directory levels in some operating systems (most notably UNIX), in addresses for gopher, and URLs (Uniform Resource Locators). For example, the following URL specifies the name and location of a hypertext version of the jargon file, which contains definitions for terms and events that have helped define the computer culture:

http://www.phil.uni-sb.de/fun/jargon/

index.html

In this URL, the file is named index.html, and it is located in the /fund/jargon directory on a machine in Germany (de).

In other operating systems, such as DOS, OS/2, and NetWare, a slash is sometimes used to indicate or separate command line switches or options for a command.

The IEEE 802.3 committee's designation for an Ethernet network that operates at 1 megabit per second (Mbps) and that uses unshielded twisted-pair (UTP) cable. This configuration uses a physical bus, with nodes attached to a common cable. AT&T's StarLAN is an example of a 1Base5 network. Also see 10BaseX; and 10Broad36.

Two dimensional.

Three dimensional.

Forth dimensional.

4B/5B encoding is a data-translation scheme that servers as preliminary to signal encoding in FDDI (Fiber Distributed Data Interface) networks. In 4B/5B, every group of four bits is represented as a five-bit symbol. This symbol is associated with a bit pattern that is then encoded using a standard signal-encoding method, usually NRZI (non-return to zero inverted).

This preprocessing makes the subsequent electrical encoding 80 percent efficient. For example, using 4B/5B encoding, you can achieve a 100 megabit per second (Mbps) transmission rate with a clock speed of only 125 megahertz (MHz).

In contrast, the Manchester signal-encoding method, which is used in Ethernet and other types of networks, is only 50 percent efficent. For example, to achieve a 100 Mbps rate with Manchester encoding, you need a 200 MHz clock speed.

A data-translation scheme that serves as a preliminary to signal encoding in 100BaseVG networks. In 5B/6B, every group of five bits is represented as a six- bit symbol. This symbol is associated with a bit pattern that is then encoded using a standard signal-encoding method, such as NRZ (non-return to zero).

A data-translation scheme related to 4B/5B encoding that recodes eight-bit patterns into 10-bit symbols. 8B/10B encoding is used, for example, in IBM's SNA (Systems Network Architecture) networks.

A tape storage format that uses nine-parallel tracks on 1/2-inch, reel-to-reel magnetic tape. Eight tracks are used for data, and one track is used for parity information. These tapes are often used as backup systems on minicomputer and mainframe systems; digital audio tapes (DATs) are more common on networks.

The designations 10Base2, 10Base5, 10BaseF, and 10BaseT refer to various types of baseband Ethernet networks.

10Base2:

(THIN - Coaxial 50 ohm) An implementation of the Ethernet IEEE standard on thin coaxial cable, a baseband medium, rated at 10 megabits per second (Mbps). The maximum segment length is 185 meters (607 feet). It is also known as thin Ethernet, ThinNet, or CheaperNet, because thin coaxial cable is considerably less expensive than the thick coaxial cable used in 10Base5 networks. See ThinNet.

(THICK - 15 Pin AUI, 50-ohm) The original Ethernet medium, an implementation of the Ethernet IEEE standard on twinaxial cable, a baseband medium, at 20 megabits per second. The maximum segment length is 500 meters (1,640 feet). See ThickNet.

10BaseF is a baseband 802.3 based Ethernet network that uses fiber-optic cable. This version can operate at up to 10 Mbps.

Standards for the following special-purpose versions of 10BaseF are being formulated by the IEEE 802.3:

• 10BaseFP (fiber passive): For desktops,
• 10BASeFL (fiber link): For intermediate hubs and workgroups,
• 10BaseFB (fiber backbone): For central facility lines between buildings.

(Twisted Pair) An IEEE standard for unshielded twisted-pair Ethernet networks. Twisted-pair cable that meets the 10Base-T standard is made up of two pairs of wires twisted around each other so that external interference is equal in each pair, minimizing its effect. 10Base-T usually uses 24 gauge unshielded, twisted-pair wiring as the baseband medium, and operates at 10 megabits per second. However, 10Base-T wiring normally called for is 26 to 22 AWG, which corresponds to the wire gauge of telephone twisted-pair cables. See Twisted-Pair Cable.

10Broad36 is a broadband, 802.3 based, Ethernet network that uses 75-ohm coaxial (CATV) cable and a bus or tree topology. This version can operate at up to 10 megabits per second (Mbps) and support cable segments of up to 1,800 meters (about 6,000 feet).

A 10Broad36 network uses differential phase shift keying (DPSK) to convert the data to analog form for transmission. Because of the encoding detials, a 10Broad36 network actually needs 18 megahertz (MHz) for each channel: 14 MHz to encode the 10Mbps signal and 4 MHz more for collision detection and reporting capabilities.

In a 10Broad36 network, throughput is 10 Mbps in each direction -- that is, a total bandwidth of 36 MHz is needed. This bandwidth can be provided in a single cable or in two separate cables. A split-cable approach uses half the cable for each direction, which means the cable must have a 36 MHz bandwidth. A dual-cable approach uses separate cables for each direction, so that each cable needs only an 18 MHz bandwidth.

10 Gigabit Ethernet is the most recent (as of 2002) and fastest of the Ethernet standards.

IEEE 802.3ae defines a version of Ethernet with a nominal data rate of 10 Gbit/sec, ten times faster than Gigabit Ethernet.

The new 10 gigabit ethernet standard encompasses seven different media types for LAN, MAN and WAN. It is currently specified by a supplementary standard, IEEE 802.3ae, and will be incorporated into a future revision of the IEEE 802.3 standard.

• 10GBASE-SR -- designed to support short distances over deployed multi-mode fiber cabling, it has a range of between 26 meters and 82 meters depending on cable type. It also supports 300 meters operation over a new 2000 MHz.km multi-mode fiber.
• 10GBASE-LX4 -- uses wavelength division multiplexing to support ranges of between 240 meters and 300 meters over deployed multi-mode cabling. Also supports 10km over single-mode fiber.
• 10GBASE-LR and 10GBASE-ER -- these standards support 10 km and 40 km respecively over single-mode fiber.
• 10GBASE-SW, 10GBASE-LW and 10GBASE-EW. These varieties use the WAN PHY, designed to interoperate with OC-192 / STM-64 SONET/SDH equipment. They correspond at the physical layer to 10GBASE-SR, 10GBASE-LR and 10GBASE-ER respecively, and hence use the same types of fiber and support the same distances. (There is no WAN PHY standard corresponding to 10GBASE-LX4.)

Unlike earlier Ethernet systems, 10 Gigabit Ethernet is based entirely on the use of optical fibre connections. Additionally, this developing standard is moving away from local area network design, with broadcasting to all nodes, towards a system which includes some elements of wide area routing. It is claimed that this system has high compatibility with earlier Ethernet and IEEE 802 networks.

10 gigabit Ethernet is very new, and it remains to be seen which of the standards will gain commercial acceptance.

A digital telephone circuit with a 64 Kbps bandwidth, but with a bandwidth of only 56 Kbps data, with the other 8 Kbps being used for signaling. Also known as a ADN (Advanced Digital Network) or a DDS (Dataphone Digital Service) line.

A digital telephone circuit with a 64 Kbps bandwidth. Also known as a DS0 (digital signal, level 0) line. When the entire 64 Kbps are allocated for the data, the circuit is known as a clear channel. This is in contrast to a circuit in which 8 Kbps are used for signaling, leaving only 56 Kbps for data.

A device for terminating wires, with the possibility of connecting input and output wires. This type of punch-down block can handle wires with up to 25 twisted pairs. The 66-type have generally been superseded by 110-type punch- down blocks.

A 100BaseT basal type variant that runs over multimode fiber-optic cable. Nodes on a 100BaseFX network can be up to 2 kilo-meters apart. This variant is also written 100Base-FX. See 100BaseT, and compare 100BaseT4; 100BaseTX.

The general name for any of three 100 Mbps Ethernet variants that have just been made a standard by an IEEE 802.3 subcommittee (802.3u). 100BaseT Ethernet is one of the candidates trying to become the standard 100 Mbps Ethernet. This version was developed and proposed originally by Grand Junction, in collaboration with several other corporations.

The term fast Ethernet is often used for this version. This is unfortunate, since that term is also used to refer to any Ethernet implementation that supports speeds faster than the oficial 10 Mbps standard. To add to the confusing terminology, a software product (no longer available) was also named fast Ethernet.

100BaseT Ethernet retains Ethernet's CSMA/CD (Carrier Sense Multiple Access/ Collision Detect) media access method -- in contrast to the 100BaseVG variant (now officially, IEEE 802.12) -- which is the other major 100 Mbps Ethernet available.

The main differences between fast (100 Mbps) Ethernet and standard (10 Mbps) Ethernet are:

• A 100BaseT Ethernet allows a much shorter gap between signals.
• A 100BaseT Ethernet requires either higher-grade cable or more wire pairs. It can run at 100 Mbps speeds on Category 3 or 4 cable -- provided four pairs are available; Category 5 cable requires only two pairs.
• Currently, a 100BaseT Ethernet can support a network that is only about a tenth of the length allowed for an ordinary Ethernet network. For networks that use copper (as opposed to fiber-optic) cabling: Two nodes of a 100BaseT4 network can be no further apart than 205 meters -- regardless of whether the nodes are next to each other.

The following variants of 100BaseT Ethernet have been defined:

• 100BaseFX: Runs over multimode fiber-optic cable. Nodes on a 100BaseFX network can be up to two kilometers apart.
• 100BaseTX: Uses two wire pairs, but requirs Category 5 unshielded or shielded twisted pair (UTP or STP) wire.
• 100BaseT4: Can use category 3, 4, or 5 UTP (Unshielded Twisted Pair) cable. The T4 in the name comes from the fact that four wire pairs are needed: two for sending and two for receiving.

In some configurations, fast and ordinary Ethernet nodes can share the same network. Fast Ethernet devices identify themselves as such by sending a series of FLPs (fast link pulses) at startup. Primary sources; IEEE 802.3u committee publications. Compare with 100BaseVG.

A 100BaseT Ethernet variant that can use category 3, 4, or 5 unshielded twisted pair (UTP) cable. The T4 means that four wire pairs are needed: two for sending and two for receiving. Two nodes of a 100BaseT4 network can be no further apart then 205 meters, regardless of whether the nodes are next to each other. This variant is sometimes written 100Base-T4. See 100BaseT. compare with 100BaseTX; and 100BaseFX.

A 100BaseT Ethernet variant that uses two wire pairs, but requires Category 5 UTP (Unshielded Twisted Pair) or STP (Shielded Twisted Pair) wire. Two nodes of a 100BaseTX network can be no further aport thn 205 meters -- regardless of whether the nodes are next to each other. This variant is sometimes written 100Base-TX. See 100BaseT, and compare 100BaseT4, and 100BaseFX.

100BaseVG is a version of Ethernet developed by Hewlett-Packard (HP) and AT&T Microelectronics, and is currently under consideration by an IEEE 802.12 committee. It is an extension of 10BaseT Ethernet that will support transmissions of up to 100 megabits per second (Mbps) over voice-grade (Category 3) twisted-pair wire. The VG in the name stands for voice-grade.

100BaseVG Ethernet differs from ordinary (10 Mbps) Ethernet in the following ways:

• Uses demand priority (rather than CSMA/CD (Carrier Sense Multiple Access/Collision Prevention)) as the media access method.
• Can use ordinary (Category 3) unshielded twisted-pair (UTP) cable, provided that the cable has at least four wire pairs. Ordinary Ethernet needs only two pairs: one to send and one to receive.
• Uses quartet signaling to provide four transmission channels (wire pairs) instead of just one. All wire pairs are used in the same direction at a given time.
• Uses the more efficient 5B/6B NRZ (Non-Return to Zero) signal encoding, as opposed to the Manchester encoding scheme used by ordinary Ethernet.
• For category 3 cable, a VG network can be at most 600 meters (1500 feet) from end to end -- and only 200 meters if all hubs in the network are connected in the same wiring closet. These values increase by 50% -- that is, to 900 and 300 meters, respectively -- when category 5 cable is used. For VG using fiber-optic cable, the most widely separated network nodes can be up to 5000 meters, or 5 kilometers, apart.

100BaseVG is designed to provide an easy upgrade path from 10 Mbps Ethernet. An upgrade requires two new components:

• A 100BaseVG network interface card (NIC) for each node being upgraded. This NIC replaces the 10 Mbps version in the node.
• A 100BaseVG hub to replace the 10 Mbps hub. This type of hub is plug-compatible with a 10 Mbps hub, so that the upgrade requires simply unplugging a node from one hub and plugging it into the 100BaseVG hub. This can all take place in the wiring closet.

If you are already using twisted-pair Ethernet cabling, you may not need any new wiring, provided that the cable has four wire pairs.

100BaseVG/AnyLAN

100BaseVG/AnyLAN is an extension of 100BaseVG, developed as a joint effort between Hewlett-Packard and IBM. This version also supports the Token Ring architecture, and it can be used with either Ethernet or Token Ring cards (but not both at the same time or in the same network). Because the demand priority access method can be deterministic, the 100BaseVG/AnyLAN architecture could handle isochronous data -- that is , data (such as voice or video) that requires a constant transmission rate.

The 100VG-AnyLAN Forum is the advocacy group for this Ethernet variant. This consortium includes over 20 members, including Apple, Compaq, and IBM. 100BaseVG/AnyLAN is also known simply as VG or AnyLAN.

See also Ethernet, HSLAN (High-Speed Local-Area Network), and compare with 100BaseT.

100BaseX (sometimes written as 100Base-X) is a function that translates between the FDDI (Fiber Distributed Data Interface) - based physical layer and the CSMA/CD - based data-link layer in a 100 megabit per second (Mbps) Ethernet proposed by Grand Junction Networks. The term was used more generally to refer to a 100 Mbps Ethernet developed by Grand Junction, amoung others. This proposed specification has since become known as Fast Ethernet, and has been refined into three variants:

• 100BaseFX, which runs over fiber-optic cable
• 100BaseT4, which runs over unshielded twisted pair (UTP) cable rated at Category 3 or higher -- provided there are four available wire pairs.
• 100BaseTX, which runs over Category 5 UTP cable.

These variants all use the standard CSMA/CD (carrier sense multiple access/collision detection) medium access scheme used by classic Ethernet. (In contrast, the 100BaseVG variant proposed by Hewlett-Packard and other companies uses a demand priority access scheme). Specifications and standards for the Fast Ethernet versions have been debated by the IEEE 802.3u subcommittee, and were just approved in June 1995. See Ethernet, Fast Ethernet, and compare with 100BaseVG.

Any of several proposed 100 Mbps implementations of the Ethernet network architecture. Three different approaches have been proposed:

• 100BaseVG,
• 100BaseX, and
• FastEthernet

These implementations differ most fundamentally in the media-access methods and types of cable they use.

A device for terminating wires, with the possibility of connecting input and output wires. This type of punch-down block has generally replaced the older 66-type blocks originally used by the telephone company. See also Punch-Down Block.

In a T1 communications channel, a framing bit that is attached to every group of 192 bits. These 192 bits represent a single byte from each of the 24 channels multiplexed in a T1 line. Also see T1.

NOTE: Many of the following 802 standards are also ISO 8802 standards. For example, IEEE 802.3 is ISO 8802.3.

The 802.1 specifies standards for network management at the hardware level, including the spanning tree algorithm. This algorithm is used to ensure that only a single path is selected when using bridges or routers to pass messages between networks and to find a replacement bath if the selected path breaks down. This document also address systems management and internetworking.

It also defines the relationship between the IEEE 802 standards and the ISO Open Systems Interconnection (OSI) reference model. For example, this committee defines 48-bit LAN station addresses for all the 802 standards so every adapter can have a unique address. Venders of network interface cards are registered and assigned the first three bytes of the address by the IEEE. Each vendor is then responsible for creating unique addresses for each of its products.

Defines the IEEE Logical Link Control(LLC) protocol, which ensures that data is reliably transmitted through a communication link. The Data-Link layer in the OSI protocol stack is subdivided into the Media Access Control (MAC) sublayer and the LLC sublayer. In bridges, these two layers serve as a modular switching mechanism. A frame arriving on an Ethernet network and destined for a token reing network is stripped of its Ethernet frame header and is packaged with a token ring header. The LLC protocal is derived from the High-Level Data-Link Control (HDLC) protocol and is similar in operation. Note that LLC provides the addresses of service access pointes (SAPs), while the MAC sublayer provides the physical network address of a device. SAPs specify the address of one or more application processes running in a computer or network device.

It is the third layer defined in the IEEE 802 LAN specifications, overlaying the 802.8, 802.4, 802.5, and FDDI protocols. 802.2, or Logical Link Control (LLC), is responsible for addressing and data link control, and is independent of the topology, transmission medium, and medium access control technique chosen. Basically, LLC provides an interface between media-access methods and the network layer. The functions provided by the LLC, which are to be transparent to upper layers, include framing (as indicated above), addressing, and error control. This sublayer is used by the 802.3 Ethernet specifications, but not by the Ethernet 2 specifications.

The standards for the LLC sublayer include specifications of the services that are provided at the interfaces between layers and sublayers of the IEEE 802 architecture. The IEEE 802 standard documents two service interface specifications:

• Network/LLC Service interface Specification. This service interface specification describes the services that define the interface between the LLC sublayer and software operating above the LLC sublayer that requests LLC services and thus services of the network as a whole. In LAN implementation that conforms to the OSI reference model, the software layer above logical link control is the network layer.
• LLC/MAC Service Interface Spedification. This service interface specification describes the services tht define the interface between the LLC and the sublayer below it, the media access control (MAC) sublayer.

The IEEE LLC standard also defines the control information attached to the data units that are passed between the LLC sublayer an the MAC sublayer. This control information is added to the data unit by the LLC sublayer prior to transmission, used by the LLC for its processing functions, and then removed from the data unit before it is passed to a higher layer at the receiving station.

LLC is that part of a data station that supports the logical link functions of one or more logical links. The LLC generates command packets or frames (called "protocol data units" or PDUs) or interprets such PDUs. In particular, the responsibilities assigned to a LLC include:

1. Initiation of control signal interchange,
2. Organization of data flow,
3. Interpretation of received command PDUs and generation of appropriate response PDUs,
4. Error control and recovery functions in the LLC.

Defined by the IEEE, these standards govern the use of the CSMA/CD (Carrier Sense Multiple Access/Collision Detection) network access method used by Ethernet networks. The standard defines networking on coaxial cable, twisted-pair cable, and fiber-optic media. The original transmission rate is 10 Mbites/sec, but newer implementations transmite at up 100 Mbits/sec on data-grade twisted-pair cable.

Defined by the IEEE, these standards govern the use of the token bus network access method. The token bus standard defines a broadband networking scheme that is used in the manufacturing industry. It is derived from the Manufacturing Automation Protocol(MAP). The network implements the token-passing method on a broadcast bus network. A token is passed from one station to the next on the network and the station holding the token can transmit. Tokens are passed in logical order based on the address of the node, but this order may not relate the physical location of the node as it does in a token ring network. The standard is not widely implemented in the LAN environment.

Defined by the IEEE, these standards govern the use of the token ring network access method. Also called the ANSI 802.1-1985, it defines the access protocols, cabling, and interface for token ring LANs. IBM made the standard popular. It uses a token-passing access method and is physically wired in a star topology but forms a logical ring. Nodes are cabled to a central access unit (concentrator) that repeats signals from one station to the next. Access units are cabled together to expand the network, which enlarges the logical ring. Fiber Distrbuted Data Interface (FDDI) was based on the 802.5 token ring protocol but was developed by the Accredited Standards Committee (ASC) X3T9. It is compatible with the 802.2 Logical Link Control layer, and thus other 802 networking standards.

IEEE 802.6 MAN defines a high-speed protocol in which attached stations share a dual fiber-optic bus using an access method called Distributed Queue Dual Bus (DQDB). The dual bus provides fault tolerance to keep connections alive if the bus is broken. The MAN standard is designed to provide data, voice, and video services in a metropolitan area of approximately 50 kilometers at data rates of 1.5, 45, and 155 Mbits/sec. DQDB is the underlying acess protocol for SMDS (Switched Multimegabit Data Service), which many of the public carriers are offering as a way to build private networks in metropolitan areas. DQDB is a cell relay network that switches fixed length 53-byte cells; therefore, it is compatible with Broadband-ISDN (BISDN) and Asynchronous Transfer Mode (ATM). The cells are switchable in the 802.2 Logical Link Control layer.

MAN services are connectionless, connection-oriented, and/or isochronous (real-time video). The bus has a number of fixed-length slots in which data is placed for transmission over the bus. Any station that needs to transmit simply places data in one or more slots. However, to accommodate isochronous time-sensitive data, slots at regular intervals are reserved to guarantee that data arrives on time and in order.

This committee provides technical advice to other subcommittees on broadband networking techniques. It is also a report from the TAG (Technical Advisory Group) on broadband networks. The document specifies the minimal physical, electrical, and mechanical features of broadband cable, and also discusses issues related to installation and maintenance of the such cable.

A group that provides advice to other subcommittees on fiber-optic networks as alternatives to existing copper cable-based networks. Proposed standards are a report from the TAG (Technical Advisory Group) on fiber-optic networks. The document discusses the use of optical fiber in networks defined in 802.3 (CSMA/CD Networks) through 802.6 (Metropolitan Area Networks (MAN)), and also provides recommendations concerning the installation of fiber-optic cable.

The IEEE 802.9 working group is working on the integration of voice, data, and video traffic to 802 LANs and Integrated Services Digital Networks (ISDNs). Nodes defined in the specification include telephones, computers, and video coders/decoders (codecs). The specification has been called Integrated Voice and Data, or IVD. The service provides a multiplexed stream that can carry data and voice information in channels connecting two stations over copper twisted-pair wire. Several different types of channels are defined including full-duplex 64 Kbits/sec nonswitched, circuit-switched, or packet-switched channels.

This group is working on the definition of a standard security model that interoperates over a variety of networks and incorporates authentication and encryption methods. It is also a report of a working group addressing LAN (local-area network) security issues, including data exchange and encryption, network management, and security in architectures that are compatible with the OSI Reference Model. An 802.9 working group has been studying the isoENET proposal, which attempts to provide bandwidth and protocol support for voice or other time-sensitive transmissions over Ethernet networks.

This committee is defining standards for wireless networks. It is working on the standardization of mediums such as spread-spectrum radio, narrowband radio, infrared, and transmission over power lines. The committee is also working on the standardization of wireless interfaces for network computing, in which users connect into computer systems using pen-based computers, personal digital assistants (PDAs), and other portable devices. Two approaches for wireless networks are planned. In the distributed approach, each workstation controls its access to the network. In the point coordination approach, a central hub attached to a wired network controls the transmission of wireless workstations. However, both distributed and point coordination approaches are both being used.

Wireless networks use signals that cover a broad frequency range, from a few megahertz to a few terahertz. Depending on the frequencies involved, the network is known as a radio wave, microwave, or infrared network.

Today the working group on wireless networking has published comprehensive specifications for wireless network architectures. Separate protocols are needed for the data-link and the physical layers.

The DFWMAC (Distributed Foundation Wireless Media Access Control) protocol was adopted in 1993 as the standard MAC (Medium Access Control) protocol. DFWMAC supports transmissions of at least 1 megabit per second (Mbps), and uses the CSMA/CA (carrier sense multiple access/collision avoidance) medium-access method, but requires acknowledgment that a transmitted packet was received.

The DFWMAC protocol can work with any of multiple physical layer protocols. These protocols are distinguished in part by the frequency band in which they are being used. The table "Frequency Band Allocations" shows the frequency bands that have been allocated (or freed) by the FCC for the specified uses.

With the help of a PCF (point coordination function), DFWMAC can even handle time-sensitive transmissions such as video. This is possible because the PCF helps grab the transmission for enough time to transmit a superframe, which contains the time-sensitive information.

FREQUENCY BAND ALLOCATIONS

This committee is defining the 100 Mbits/sec Ethernet standard with Demand Priority access method proposed by Hewlett-Packard and other vendors. The specified cable is 4-wire copper twisted-pair and the Demand priority access method uses a central hub (STAR Topology) to control access to the cable. Priorities are available to support real-time delivery of multimedia information.

This architecture supports speeds of up to 100 Mbps, but uses a different media access scheme than the Ethernet versions defined by 802.3 committees. In June of 1995, the 802.12 committee adopted 100BaseVG as a standard. This is one of the two 100 Mbps standards adopted at that time. The other was the 100BaseT, adopted by 802.3u.

FireWire. A low- to medium-speed bus intended for desktop PC implementations. It appears that 1394 will be used mainly in consumer audio/video products, set- top (cable) boxes, scanners and printers.

In IBM's SNA (Systems Network Architecture) environment, a stream in which characters are converted and/or formatted, as specified through control characters and attribute settings.

This is the numicalture used for a cluster controller that can serve as a front end for an IBM mainframe host. Devices, such as 3270 terminals or printers, communicate with the host through this controller. The 3274 cluster controllers have been replaced by 3174 establishment controllers in newer configurations.

The designation for a popular IBM terminal used to communicate with IBM mainframes.

The designation for a color version of the 3278 terminal used to communicate with IBM mainframes.

The designation for a computer that serves as a data communications controller for IBM's 370-series mainframes. The 3705 also has ports for asynchronous access over dial-up lines.

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